Webbased GUI for creating/modifying workflow

Iam newbie to workflow systems. We need to develop a simple workflow as per business requirements and that needs to be integrated with an existing system. As a developer I can use any of the open source workflow engines available such as jBpm and can accomplish this task. Apart from this we need to provide a GUI where user could define/modify a workflow [ drag and drop interface as in case of jBpm eclipse plugin ] deponding on his/her role. We need this as business requirements are quite dynamic causing an impact on existing workflow definition. Whether any workflow ystem supports this type of web-based GUI for editing/modifying a workflow ? Or we need to define a new workflow when business flow changes?